Transparent electrodes are indispensable elements in display devices such as thin-screen televisions, cellular phones, smartphones and tablets, as well as in touch panels, solar cells, electroluminescent elements, electromagnetic shieldings, functional glass and the like. The primary conducting material for transparent electrodes used in such electronic devices is indium tin oxide (hereunder abbreviated as “ITO”).
However, because the indium starting material for ITO is a rare metal, there are concerns with regard to future supply. Furthermore, it has been difficult to reduce costs due to the low productivity in steps such as sputtering for fabrication of ITO films, and a substitute material for ITO has therefore been desired.
New transparent conductive materials that can serve as ITO substitutes have been proposed in recent years, such as transparent conductors with patterned conductive layers that contain metal nanowire materials as well as methods for producing them, as described in Patent Literature 1, for example. Transparent conductive films with transparent conductive layers containing fibrous conductive substances, such as carbon nanotubes or conductive polymers, have also been studied and are described in Patent Literature 2, for example.
These exhibit high transparency and low electrical resistance on a level that can substitute for conventional ITO films, but with transparent conductive films having transparent conductive layers that employ fibrous conductive substances such as metal nanowires or carbon nanotubes, the fibrous conductive substance is in the form of rod-like shapes with limited lengths, and therefore the fibrous conductive substance tends to align in a certain direction during the production steps, readily resulting in anisotropy of the electrical characteristics or optical characteristics of the transparent conductive film. As a result, the electrical characteristics and optical characteristics differ depending on the location and orientation of the transparent conductive film, thus potentially adding the problem of visibility to the other difficulties in terms of quality control. In addition, because of the limited lengths, there are few points of contact between the fibrous conductive substance, i.e. few conductive paths, and it is not possible to adequately exhibit the electrical characteristics of the fibrous conductive substance.
In order to eliminate the anisotropy of properties in transparent conductive films, as represented by Patent Literatures 1 and 2, research has been conducted on transparent conductive films wherein a regular conductive metal mesh pattern is formed to avoid producing anisotropy in the characteristics of the transparent conductive film (Patent Literature 3). However, due to the regularity of the conductive metal mesh pattern, an inherent problem is faced in the tendency toward moire pattern formation.